The invention relates to an actuator for a vehicle door latch and particularly, but not exclusively, for use in a vehicle, where the latch forms part of a vehicle central and/or remote locking system.
There are, principally, two methods of latch actuation known in the art. The two methods are distinct in the way a relative movement is generated in the transmission path between an actuator power source, usually a DC motor, and a latch mechanism. This relative movement allows the latch mechanism to be manually locked without requiring back driving of the power source.
In the first method, the relative movement is generated by a centrifugal clutch arranged between the DC motor and the latch mechanism.
In the second method, the latch mechanism is driven by the DC motor via a lever that is movable within a lost motion space before engagement with the latch mechanism. The lever is biased to a rest position between two outer positions that correspond to a locked and an unlocked status of the latch mechanism. Upon locking a master door, the DC motor in each of the slave doors drives the lever to a physical stop corresponding to the locked position. With the lever driven to the physical stop, the DC motor remains in a stalled state for a fixed period of time, typically between 0.1 and 0.8 seconds. The power to the DC motor is then stopped and the lever is returned to an intermediate rest position by a biasing member.
However, both of these methods of actuation have distinct disadvantages. In both methods, the DC motor is repeatedly driven to stall, increasing motor fatigue and reducing reliability. A further disadvantage of the first method is that the DC motor must overcome the friction of a centrifugal clutch. Likewise, in the second method, the DC motor must load the biasing member before the latch mechanism is actuated. In both methods, this results in poor efficiency of actuation.